"We discovered a number of trends in the results that paint a compelling picture of volunteering as an important lifestyle component for maintaining health and well-being in later years," said lead investigator Nicole Anderson from the University of Toronto in Canada.

Feeling appreciated or needed as a volunteer appears to amplify the relationship between volunteering and psycho-social well-being.

More vulnerable seniors (those with chronic health conditions) may benefit the most from volunteering.

However, health benefits depend on a moderate level of volunteering.

There appears to be a tipping point after which greater benefits no longer accrue. The "sweet spot" appears to be at about 100 annual hours, or two to three hours per week.

"Taken together, these results suggest that volunteering is associated with health improvements and increased physical activity - changes that one would expect to offer protection against a variety of health conditions," Anderson added.

For the study, the researchers examined 73 studies published over the last 45 years involving adults aged 50-plus who were in formal volunteering roles.